Piston



May 9, 1961 CHI M. TSANG 2,983,565

PISTON Filed NOV. 27, 1959 6' 1 VENTOR. @Z ("/2% Z6250 United States PISTON.

Chi M. Tsang, Warren, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 27, 1959, Ser. No. 855,865

Claims. Cl. 309-12 This invention relates to internal combustion engine skirted pistons and more particularly to means in such pistons to increase the effective diameter of the piston skirt and thereby compensate for increases in the clearance betweenthe skirt and the cylinder walls occurring during piston operation and as a result of wear between the piston and cylinder.

One of the principal objects of this invention is to provide a piston so constructed that the desired clearances between the bearing faces of the skirt and the cylinder wall may be maintained through the operating range of the engine. 7

The above and further objects of the invention will appear more fully from the following description taken in conjunction with the drawing in which:

Figure 1 is a view in elevation with parts in section showing a horizontally slotted trunk type piston with the invention applied thereto; i

Figure 2 is a view in plan also with certain parts shown in section taken substantially on the line 2-2 of Figure 1;

Figure 3 is a diagrammatic view of the upper part of the piston skirt illustrating the effect of certain external forces, such as pressure onthe piston head and forces on the wrist pin; and

Figure 4 is a perspective, fragmentary view of the piston skirt adjacent its upper end in the area of a thrust face thereof showing the anchoring means for the ends of an expander spring forming an important element of the invention.

Referring now to the drawing, a piston 2 is shown which includes an upper head 4 and a downwardly depending skirt 6. The piston head 4 is separated from the upper end of the skirt 6 in the area of the thrust faces 8 by a pair of horizontally extending slots 10. The slots 10 terminate adjacent piers 12 which serve to connect the piston head 4 to the skirt 6 and the wrist pin bosses 14.

Patented May 9, 1961 sulting in greater clearance between the thrust faces 8 of the piston and the cylinder in which it operates.

In order to compensate for this added clearance resulting from the conditions previously mentioned, a leaf spring 1-6 has been mounted in the piston beneath the piston head at 90 degrees to the axis of the wrist pin bosses. There are three contacting areas between the leaf spring 16 and the piston, namely at the center of the spring indicated by the numeral 18 on its convex side and also at its two ends 20 and 22. As already mentioned, the convex side of the spring 16 contacts the lower surface 18. In the example shown, the lower surface is formed on a reinforced rib on the underside of the piston head and the surface is machined by a formed cutter to form a spherical surface so that the contacting surface 18 will conform with the outer convex surface of the spring.

The piston, as thus far described, is conventional in that i it is a typical horizontally slotted trunk type piston for an internal combustion engine.

In this type of piston there are certain forces acting thereon which tend to hoopstretch the piston skirt along the axis of the'p in bosses causing the thrust faces of the piston 8 to draw somewhat closer together so that as the piston moves up and down in its cylinder, unless compensating means are provided, piston slap occurs. stretching action is the pressurein the upper side of the piston head which causes the piston to elongate along the wrist pin axis adjacent the upper end of the skirt. Another is that the forces of the connecting rod on the wrist pin and, consequently, on the bosses and other parts of the piston due to gas pressure on theupper side of the piston One of the reasons for this so-called hoop.

This has been done in order that the contacting area between the spring and the head is the maximum to thereby provide better heat conduction and smaller bearing pressure, the latter thus reducing wear. It also facilitates assembly of the piston as will appear later.

Adjacent the upper end of the piston skirt 6 inboard of the oppositely disposed thrust faces 8 is a pair of oppositely disposed shoulders 24 which have formed therein cylindrical sockets 26 for receiving the semi-cylindrical ends 24) and 22 of spring 16. Extending through the skirt wall adjacent opposite ends of each of these shoulders 24 is a pair of holes 28 which are for the purpose of inserting suitable tools to finish the cylindrical bearing surfaces 26 if that is deemed necessary.

In order to assemble the leaf spring in the piston skirt, it is placed inside the skirt in an angular position and compressed toward the piston head until both ends lie between the shoulders 24 and the piston head as indicated by the dotted lines in Figure 2. When the spring is in this position it can be turned on the spherical bearing surface 18 until the spring is turned 90 degrees from the axis of the pin bosses. Compression may then be released and the spring will lock itself in the position, shown in solid lines in Figures 1 and 2. In this position the spring is only slightly compressed.

The operation of the spring 16 in the piston skirt 6 is as follows. At the end of the compression stroke or just before top dead center, the pressure inside the cylinder is already high due to compression or spark advancement. This pressure acting on the head of the piston will tend to deflect the latter downwardly causing the hoop stretch action of the skirt indicated in Figure 3. downwardly acting pressure on the head of the piston will also cause the surface 1% to move downwardly thus exerting horizontal forces at the ends 20 and 22 of the spring on the upper end of the skirt of the piston in the area of the thrust faces thereby compensating for the hoop stretch action created by the pressures on the upper side of the head of the piston 4. Because of this compensation, when the thrust from the connecting rod on the wrist pin in the bosses 14 changes from one side of the cylinder to the other, thcre is little or no piston rocking or slapping. By properly selecting the spring rate and initial compression of the leaf spring, the clearance between the skirt, the

piston and the area of the thrust base and the cylinder can be eliminated or diminished to the proper amount whether the engine is cold or hot. Should wear occur between the upper end of the skirt and cylinder the initial compression of the spring will compensate for this wear by pushing the skirt in the area of the thrust'faces slightly outward. By properly choosing the bearing pressure existing between the end of the spring and the shoulders on the spring and also existing on the top of the leaf spring'in the lower surface 18 of the piston head and with the splash lubrication already available inside engines in However, this which such pistons are used, this device can be made to operate throughout the life of the engine.

In addition to the advantages already mentioned for l. A skirt expander'for a piston having a head andskirt adapted to engage the underside of the piston head, and having ends including means for anchoring said ends to the piston walls forming the skirt in the area of the thrust faces of the piston so that pressures on the piston head act through the spring to expand the walls of the piston in the area of the thrust faces.

2. An internal combustion engine piston comprising a head and a skirt partially separated by horizontal slots in the area of the thrust faces of the skirt, and means for expanding the skirt near the thrust faces comprising'a spring element inside the skirt facing convexly upwardly and having its opposite ends anchored to the skirt in the area of the thrust faces, the head of said piston having a surface on the underside thereof engageable with the convex side of said spring intermediate the ends thereof so that when said piston head is subjected togaseous pressures said spring causes expansion of said skirt in the area of the thrust faces.

3-. The combination of claim 2 in which the surface on the underside of the piston head is spherical.

4. The combination of claim'3 in which the inside walls of the piston skirt in the area of the thrust faces are provided with shoulders having cylindrical surfaces formed therein for reception of cylindrical surfaces provided on the ends or' the spring. 7' I v 5. The combination of claim 2 in which the inside walls of the piston skirt in the area of the thrust faces are provided with shoulders having cylindrical surfaces formed therein for the reception of cylindrical surfaces provided on the ends of the spring.

References Cited in the file of this patent UNITED STATES PATENTS 1,739,792 'Haight Dec. 17, 1929 2,122,729 Smith July 5, 1938 2,180,428 Phillips Nov. 21, 1939 UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent No. 2,983,565 May 9 1961 I Chi M Tsang It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 63 for 'in" read me on column 4t line 7, for the claim reference numeral "3" read 2 e; line l2. for the claim reference numeral 2' read 3 o Signed and sealed this 2nd day of January 1962a (SEAL) Attest:

ERNEST W, SWIDER DAVID L. LADD Attesting Uffieer Commissioner of Patents 

